There was a friend of mine that wanted to install a projector in his son’s room so he could watch movies. Normally this would be suspended from the ceiling per the layout of the room. However, given the boy’s age I wondered how he would jump on his bed without injuring himself.

At first I thought perhaps mounting it in the upper corner of his room, angled to the far wall. But again it may have been hit by a stray ball or other flying object given the playful nature of the inhabitant.

Finally I settled that it must retract so as not to pose any undue hindrance to fun.
I have found such a design here: